Tennessee state flags and Capitol Building, seen along the Pathway of History in The Bicentennial Mall State Park. FileJohn Cardasis / Getty Images

May 9, 2017, 12:25 AM GMT / Updated May 9, 2017, 12:25 AM GMT

By Mary Emily O'Hara

Four married lesbian couples, each expecting children in the fall, have filed a lawsuit against Tennessee over the state's new "Natural and Ordinary" language law.

The law signed Friday by Gov. Bill Haslam mandates that all words in the state's various legal codes be interpreted to have "natural and ordinary" meanings — including words like "wife" and "mother," which the couples say could interfere with their parental rights.

The law, which seems vague and semantic at first glance, came after conservative legislators filed a motion to intervene in a high-profile lesbian custody battle in Knoxville last fall. A handful of bills proposed in January sought to restrict the definition of terms like "husband" and "wife" in response — and while Senate Bill 1085 never specifically mentions LGBT couples, critics and supporters alike have pointed out its intent.

"Undefined words shall be given their natural and ordinary meaning," the law reads, "Without forced or subtle construction that would limit or extend the meaning of the language, except when a contrary intention is clearly manifest."

The lawsuit was filed Friday in Davidson County Chancery Court in Nashville by attorney Julie Tate-Keith. She's representing Charitey and Heather Mackenzie, Crystal Dawn and Terra Mears, Elizabeth and Heather Broadaway, and Kathrine and Emilie Guthrie. All four couples have one pregnant partner due to give birth this fall.

"The Supreme Court said that gay people could get married," Tate-Keith told NBC News Monday. "If that’s to be meaningful, then same-sex couples have to be treated the same way that opposite-sex couples are, and that means parentage just like anyone else."

Some lawmakers have denied that the law is directed at curbing LGBT rights. The bill's Republican sponsor, Andrew Farmer, told NBC News in late April that the legislation has "nothing to do with same sex marriage or gender."

But even the state's Republican Attorney General, Herbert Slatery, noted that the 'Natural and Ordinary' language law could be a kind of workaround for same-sex marriage rights.

He was referring the U.S. Supreme Court's 2015 decision in Obergefell v. Hodges, which made same sex marriage legal across the nation.

Tate-Keith scoffed at the idea that Tennessee's new law was anything but an attack on LGBT couples, saying that multiple senators and the attorney general argued about the law's impact on Obergefell. Gov. Haslam also mentioned it in a statement on Friday, the day he signed the bill into law.

"If this isn’t about gay people," asked Tate-Keith, "Why are we talking about gay people?"

Besides the law's intent, the attorney said, it's clear that same-sex couples and parents will be affected.

Under Tennessee law, a "child born to a married woman as a result of artificial insemination, with consent of the married woman's husband, is deemed to be the legitimate child of the husband and wife." After the Supreme Court's Obergefell ruling legalizing same-sex marriage, Tennessee interpreted "husband" to include the female spouses of lesbians.

All of that could change under the new law, which says that "husband" means only one thing — the male husband of a female wife.

Tate-Keith and her four clients want the law overturned, and a court order that clarifies that married same-sex couples and their children are to be treated the same as heterosexual families under the law.

If they aren't successful, the LGBT families in Tennessee could face obstacles when it comes to custody, health insurance, social security, traveling across state lines, and more, says the lawsuit.

Chris Sanders of the Tennessee Equality Project told NBC News he's not surprised that a lawsuit was filed just one business day after the governor signed the bill.

"These parents wasted no time protecting their families," said Sanders. "We are hopeful that they will prevail in court."